The present invention relates to a studless tire having a plurality of block rows in the tread portion, and more particularly to a studless tire capable of suppressing a vehicle from staggering at the time of braking on an icy road and a snow-covered road to stabilize the posture of the vehicle.
Various studless tires suitable for traveling on icy and snow-covered roads have been proposed, for example, in JP-A-9-323511 and JP-A-2006-76556. A plurality of blocks provided with a large number of sipes are formed in the tread portion of studless tires. The coefficient of friction between the blocks and an icy road is enhanced by the edges of sipes. The sipes also serve to absorb a thin water film on an icy road into the gaps of the sipes. By a synergistic action of them, studless tires can exhibit both sufficient driving force and braking force on an icy road.
However, even studless tires have a problem that a vehicle is easy to stagger or sideslip on icy and snow-covered roads at the time of driving or braking. For example, a vehicle tends to sideslip when tires are locked during straight running on an icy or snow-covered road.
Accordingly, it is an object of the present invention to provide a winter tire called studless tire which can suppress a vehicle from staggering or sideslipping at the time of braking on icy and snow-covered roads.
This and other objects of the present invention will become apparent from the description hereinafter.